Most negative glow discharge lamps typically employ a mercury fill material which emits ultraviolet radiation upon excitation, in combination with a noble gas such as neon. The ultraviolet radiation is then converted into visible light by a phosphor coated envelope. The following are typical samples of mercury negative glow discharge lamps disclosed in the prior art: U.S. Pat. Nos. 4,521,718; 4,518,897;4,516,057; 4,494,046; 4,450,380; 4,413,204. Among other things, it is noted that with lamps of this type there is energy loss associated with the aforementioned conversion process and an inefficient energy transfer results.
In addition to the aforementioned mercury glow discharge lamps, the prior art also discloses a low pressure sodium lamp. These lamps operate in the positive column regime and one drawback associated with these lamps is that they only discharge yellow light within the visible spectrum due to the use of low energy excitation electrons. Thus, a very narrow spectral arrangement exists with these lamps and they are not generally effective in providing "white" light.
In the book "Introduction to Electrical Discharges in Gases" (Wiley & Sons, 1966, N.Y.) by Sanborn C. Brown, in Chapter 13 thereof under "Glow Discharges" there are described certain parameters relating to glow discharge lamps. They describe the color of the negative glow regime of a sodium discharge as being "whitish." This book suggests the use of sodium in a glow discharge lamp only in connection with cold cathode operation. These lamps are characterized by a relatively narrow spectral response.